added spec for issue #51
added additonal slice specs
more slice spec fixes
Elementwise operations fixed on dense matrices for bug in #51.
Fixed transposes on slice-by-reference dense matrices.  (Fixes #51.)
fix memory leak in tranpose of slice by reference
added spec for each and each_stored_with_indices on sliced by reference dense matrices
fixed slice by reference issue with each and each_stored_with_indices
changed calloc calls to ruby alloc macros
added null check to deletion code and changed each iterators to pass NULL for elements
Merge pull request #80 from cjfuller/ref_slice_ops_issue51

Fixes for #51-related elementwise operations on dense matrix slices.